Reset circuits are used to monitor power supplies in microprocessors, digital equipment, and various other electronic equipment and systems. A reset circuit is used to assert a reset signal whenever the supply voltage falls below a determined threshold voltage and to de-assert said reset signal when the supply voltage rises above a threshold. This reset signal may be input to the microprocessor, for example, to start the microprocessor in a known state during power up to prevent code execution errors, during power down to initiate a clean shutdown sequence, and during brownout to achieve control over marginal voltage conditions.
One deficiency of reset circuits is that proper assertion of reset signals during power down conditions may not reliably occur. The power supply voltage may decrease so quickly that existing reset detection circuitry may cease functioning before outputting a valid (changed) reset state.